Navigation bar button appears with delay in mixed UIKit and SwiftUI project

Question

I have an app which main framework was developed using uikit, and some of its pages were written by SwiftUI and embedded into uikit for display through UIHostingController. Now there is a Swiftui page, and I want to push to this page by UIHostingController.

The window init code is as bellow:

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        window = UIWindow(frame: UIScreen.main.bounds)
        
        let vc = UINavigationController(rootViewController: ViewController())
        
        window?.rootViewController = vc
        window?.makeKeyAndVisible()
        return true
    }

Then is the SwiftUI View:

struct ContentView: View {
    var body: some View {
        Text("hello world")
    }
}

Then is the UIKit vc:

import UIKit
import SwiftUI

class ViewController: UIViewController {
    
    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .white
        view.addSubview(runBtn)
        runBtn.frame = CGRect(x: 100, y: 200, width: 200, height: 50)
    }
    
    lazy var runBtn: UIButton  = {
        let btn = UIButton()
        btn.setTitle("Push to SwiftUI View", for: .normal)
        btn.setTitleColor(.blue, for: .normal)
        btn.addTarget(self, action: #selector(runBtnAction), for: .touchUpInside)
        return btn
    }()
    
    @objc func runBtnAction() {
        let contentView = ContentView()
            .toolbar {
                ToolbarItem(placement: .automatic) {
                    Button {
                        //isShowSettingView = true
                    } label: {
                        Image(systemName: "ellipsis.circle")
                    }
                }
                ToolbarItem(placement: .automatic) {
                    Button {
                        //addItem()
                    } label: {
                        Image(systemName: "square.and.pencil")
                    }
                }
            }
        let vc2 = UIHostingController(rootView: contentView)
        vc2.title = "Hello"

        navigationController?.pushViewController(vc2, animated: true)
    }
}

After click the button, it can push the SwiftUI View. However, the two buttons in the upper right corner will only be displayed after a short delay. How can I solve this problem? How can it be displayed directly instead of flashing.